The analog-to-pulse integrating converter (APIC) is a new and improved circuit. The APIC circuit is an innovative means of accomplishing analog voltage-to-pulse rate conversion, and as such, could find more general usage in digital transmission, electronic testing, and telemetering applications.
Since the primary use of the APIC circuit is in interfacing analog DC voltages with digital computers, its design approach and characteristics can be compared with both standard analog-to-digital converters and with other devices yielding a pulse rate output for a DC input. The comparison will enable one to appreciate the unique design features and resulting advantages of the APIC circuit described in this invention disclosure.
Standard analog-to-digital converters can provide an almost continuous digital parallel output proportional to a DC input. For more than one input, multiplexing can be used to reduce the number of converters necessary. The accuracy of the parallel converter, however, is limited by the maximum number of output bits and circuit noise. To obtain 0.05 percent resolution, a 12-bit converter must be used; if greater resolution is required, converters with even more bits are needed. Standard converters of more than 12-bit range tend to be expensive. Greater resolution is even harder to obtain and approaches the state-of-the-art for this type of equipment.
In applications where the input signal can be integrated. the conversion and integration can be accomplished simultaneously, resulting in a pulse train output where the number of pulses represent the integral of the DC input. By doing this, the resolution obtainable is limited only by the range of the device counting the pulses, the converter component errors and the integrated signal noises.
The present APIC circuit 1) has its output synchronized with an applied clock signal; 2) applies the voltage reset function at a constant amplitude and width by using voltage regulation and analog switching techniques; 3) operates on a bipolar input yielding a bipolar output with a zero mean, and 4) has the capability for independent positive and negative scale factor adjustments. In addition, by using an input to the pulse generating flip-flop reset terminal, the APIC output pulses can be time-correlated with a digital input function such as a computer clock. This will enable synchronization of pulse output times and computer interrupts so that additional peripheral input logic would not be necessary in this instance.
Due to these design features, the APIC circuit possesses higher accuracy and less temperature and voltage sensitivity than other comparable devices. Representative conversion circuit claims show accuracies of no less than 0.01 percent, while tests have shown the APIC accuracy to be at 0.009 percent.